Vibration resistant electron tube



Feb. 14, 1967 H. LANGER ETAL 3,304,458

VIBRATION RESISTANT ELECTRON TUBE Filed July 25, 1963 HELMUT LAM/GER 50M0 J. KULOW/EC United States Patent 3,304,458 VIBRATION RESISTANTELECTRON TUBE Helrnut Langer, Stamford, and Edmund J. Kulowiec,

Springdale, Conn, assignors to The Machlett Laboratories, Springdale,'Conm, a corporation of Connecticut Filed July 25, 1963, Ser. No.297,597 6 Claims. (Cl. 313-269) This invention relates to electron beamtubes and has particular reference to such tubes having novel electrodesand mounting structures therefor which permit operation under severevibration conditions and with relatively low drive power.

A serious problem in the manufacture of electron tubes is to provide atube which will operate efficiently under severe vibration conditionssuch as are encountered in some industrial applications or in missileinstallations. Such tubes must be rugged to withstand vibration" butshould preferably also be so constructed that driving power is low toobtain maximum operational efiiciency.

In accordance with this invention the electrode structures within thetube envelope are so constructed and mounted that motion is considerablydamped. This, combined with resonant frequencies of the electrodemembers which are of high values, produces eflicient operationalstability of the tube during vibration. For example, a tube constructedand arranged as taught herein should be capable of operating as a pulseswitch tube at 300 kilowatts peak output with a duty of .001, and shouldoperate stably at 10 g acceleration for a 50-2000 c.p.s. range atconstant output power. We have made our tube with electrode structureswhich are as short as possible without interfering with the operationalcharacteristics required of the electrodes, thus considerably increasingthe resonant frequencies, and have rigidized the structures to furtherdamp vibratory motions in a novel manner.

Accordingly, it is a primary object of this invention to provide animproved beam type electron tube which will operate efficiently undersevere vibration conditions.

Another object is to provide an electron tube of the above characterwherein the electrode structures are provided with sufliciently highresonance frequencies such as will not affect the stability of operationof the tube during vibration.

Another object is the provision of an electron tube having novel andextremely rugged electrode supporting structures.

A further object is the provision of novel means in an electron tube forrigidizing electrode structures and preventing relative movementstherebetween.

A still further object is to provide novel means for supportingelectrodes upon terminal mounts whereby expansion of parts during tubeoperation will cause increase in the ability of the parts to resistrelative movements when subjected to severe vibration conditions.

Other objects and advantages of the invention will become apparent fromthe following description taken in connection with the accompanyingdrawings, wherein:

FIG. 1 is an axial sectional view of an electron tube embodying theinvention;

FIG. 2 is an enlarged fragmentary horizontal sectional view takensubstantially on line 22 of FIG. 1;

FIG. 3 is an enlarged fragmentary transverse sectional view of a portionof the electrode structures;

FIG. 4 is an enlarged fragmentary view of the supporting structure forthe shield grid; and

FIG. 5 is a reduced front elevational view of the screen grid.

Referring more particularly to the drawings, the tube embodies avacuum-tight envelope which includes a glass bulb 10, at one end ofwhich is mounted an anode 11, and supporting at its other end a cathode12, a cathode heater 13, a control grid 14 and a screen grid 15.

A relatively short metal cylinder 16 is sealed at one end to the anodeend of the bulb 10 and has its other end sealed to an inversefrusto-conical member 17 which closes the end of the envelope. Member 17is relatively thick and because of its shape is not sensitive tovibrations. The member 17 may carry a suitable exhaust tubulation (notshown) if desired as a means whereby the envelope may be evacuated.

The anode 11 is a hollow cylinder which has one end sealed to the innersurface of Kovar cylinder 16 and extends inwardly therefrom toward theopposite end of the tube. Means such as a bead 18 may be provided tostilfen the intermediate wall portion of the anode cylinder 11 as wellas the open end portion 19 thereof to eliminate any frequency modesduring vibration. Cylinder 11 is further rigidized by a conical portion20 which also permits the major portion thereof to assume a largerdiameter than the end portion which is joined to the Kovar cylinder 16.

The other end of the bulb 10 is sealed by a second metal cylinder 21 toan inverse substantially conically shaped support or terminal member 22which has a central bore within which is fixedly located one end of acylinder or block 23 of nonconductive insulating material such asceramic. The cylinder 23 is of substantial size and has a coefficient ofexpansion greater than that of the closely encircling support member 22.Thus, when heated during operation of the tube, the cylinder 23 willexpand to such a degree as to place itself under compression by moreclosely engaging member 22 and in this way will suppress resonances inthe terminal mounting structure during vibrations of more than 2000c.p.s.

One end of a metal frusto-conical ring 24 is brazed or otherwise affixedto the upper surface of member 22, and carries on its opposite end thehollow cylindrical cathode 12. The cathode is open at the end which isjoined to ring 24 but the other end is sealed by a cap 25 through whichextends a central axially extending nonconductive ceramic pin orcylinder 26. The cathode is adapted to be provided with a predeterminedelectrical potential from terminal 22 through the ring 24.

The outer surface of the cathode 12 is provided with a plurality ofspaced longitudinally extending grooves 27 (FIG. 3), and alternategrooves are each provided with a selected heat-sensitiveelectron-emissive material 28 such as one of the oxides commonly usedfor this purpose in the electron tube industry and which, when subjectedto heat, is capable of emitting copious supplies of electrons which aredirected toward the anode 11.

The means for heating the cathode 12 to the elevated temperaturesrequired for liberation of electrons includes the heater 13 locatedinteriorly of the cathode 12 and comprising a relatively open mesh ofwires, preferably tungsten, supported at the lower end of the structureby a metal cup 29. Cup 29 is firmly attached to an eyelet 30 fixedlymounted on one end of a thin pin or shaft 31 which extends through theceramic cylinder 23. The other end of shaft 31 is fixed :to a ring 32which :is fixed to the inner side of a closure member 33 forming a partof the envelope. To the outer surface of the closure member 33 andopposite the ring 32 is affixed a heater terminal 34 which may take theform of a tube, as shown in FIG. 1.

The other end of the heater 13 is fixed :to a cap 35 which has a centralopening in which is located one end of the ceramic pin 26, the cap beingprovided around the opening with a flange which bears snugly throughoutits inner surface upon the pin 26 and which projects through theadjacent opening in the end cap 25 of the cathode cylinder 12. In thisway the cathode forms one side of the circuit through the heater, andwhen the ceramic pin 26 is expanded by heat it will cause increased apressure between the flange and cap 25, thereby providing betterelectrical contact and rigid support of the parts.

Means may be provided externally of the envelope for aiding in thedissipation of heat from the shaft 31, closure member 33 and terminal 34such as by attaching a radiator (not shown) to the end of the terminal.In order to confine the heat from the heater within the effectiveportion of the cathode, disc-like heat reflectors or bafiles 36 aremounted over the eyelet 30 as shown in FIG. 1. Thus, heat attempting toescape through the open end of the cathode cylinder is reflected backinto the interior. Heat losses are further reduced by the use of a shaft31 which is of relatively small diameter and which thus forms a thermaldam.

The control grid 14 encircles the cathode and is comprised of spacedgrid members 37 (FIGS. 2 and 3) which extend parallel to the cathode andto each other and in predetermined spaced relation to respectivenonemitting portions of the cathode. Members 37 are channelor U- shapedso as to be mechanically rigid under vibration and are formed of thinsheet material, such as sheet molybdenum, whereby the weight of eachmember 37 as well as of the entire control grid is considerably reduced,increasing the resonant frequency of the structure by several factors.An additional advantage achieved by a grid member of this shape is theenlargement of the radiating surface area compared with the surface areaof solid members. This provides improved electron beaming and a highamplification factor which decreases driving power.

The upper ends of the grid members 37 are brazed to a cap 38 which has acentral opening for snugly receiving the ceramic pin 26, and the lowerends are fixed to tubular ring 39 which is mounted firmly in the ends ofa number of rugged posts 40. Posts 40 project freely through respectiveopenings in the cathode terminal 22 and are firmly mounted in an annularfrusto-conical support 41 which has a central opening snugly embracingthe ceramic cylinder 23. To provide additional support for the controlgrid and to provide means for conducting electrical potential thereto,the periphery of support 41 is fixed to the inner end of an axiallyextending tubular member 42, the outer end of which is fixed to a heavyring-type terminal 43.

Closing the envelope outwardly of member 42 is an encircling glass ring44 which is sealed at each end by metal rings 45 and 46 to the cathodeand control grid terminals 22 and 43 respectively. The envelope issimilarly closed inwardly of member 42 by glass ring 47 which is sealedat one end to the closure member 33 and at the other end by a metal ring48 to the terminal 43.

The shield grid 15 which encircles the control grid 14 comprises aplurality of flat wire elements 49 which are radially spaced outwardlyof respective control grid members 37 and extend parallel thereto. Theupper ends of the elements 49 are brazed or otherwise fixed to a cap 50which also has a central opening snugly receiving the ceramic pin 26.The shield grid is operable at cathode potential and, therefore, ismounted upon the cathode terminal 22 by means of a substantiallyfrusto-conical support 51 to which the lower ends of elements 49 arefixed. Support 51 is shaped to interfit closely over a sizablecircumferential surface portion of terminal 22 and is held firmly inplace by a number of elongated tabs 52 which are each brazed along oneedge to the cathode terminal 22 adjacent the lower end of the gridsupport 51 and are bent into overlying relation to support 51 as shownbest in FIG. 4. Support 51 is provided with a number of recesses orslots 53 in which indented portions of the tabs are located so as toprevent respective rotary movements of the parts and also to furtherrigidize the structure. The height of tabs 52 is somewhat greater thanthe height of the surface portion of the terminal 22 which is engaged bythe support 51. Thus, the process of bending the tabs inwardly towardthe axis of the structure tends to still more firmly secure the grid inplace upon the terminal, thus dampening vibrational resonances in thestructure.

One or more spaced spirals 54 (FIG. 5) of relatively fine wire is woundaround the outside of the shield grid 15 and welded to each grid element49, thus effectively dampening torsional movements during vibration.

A tubular shield 55 is attached at one end to the cathode terminal 22 orto the cylinder 21 at the joint therebetween and extends toward theopposite end of the tube beyond and spaced outwardly of the adjacent endof the anode 11. This protects the glass-metal seals from possibledestruction by high voltage field concentrations.

It is particularly pointed out that horizontal and vertical movements ofthe grids, cathode and heater with respect to each other are effectivelyprevented by the novel employment of the ceramic pin 26 and the ceramiccylinder 23. Furthermore, the pin 26 and the cylinder 23 provideaccurate and constant spacing between the electrodes, with cylinder 23,particularly, being of substantial size and strength and mounted so asto contribute to the rigid support of the cathode and grids whereby theyare relatively unaffected by vibrations, with the suppression ofresonances, during vibration, of more than 2000 c.p.s. underacceleration forces of 10 g. and more.

Furthermore, the overall electrode structures are relatively short inlength and large in diameter to obtain sufiiciently high resonancefrequencies which will not affect operational stability of the tubeduring vibration.

From the foregoing it will be apparent that a novel tube has beenachieved in accordance with the objects of this invention. It is to beunderstood, however, that modifications and changes may be made by thoseskilled in the art without departing from the spirit of the invention asexpressed in the accompanying claims.

What is claimed is:

1. An electron tube comprising a glass bulb, a relatively heavysubstantially frusto-conical end member sealed to one end of the bulb, atubular anode mounted at one end adjacent the seal between the endmember and bulb, an inverse relatively heavy frusto-conical terminalmember sealed to the opposite end of the bulb, a pair of rigidsubstantially frusto-conical inwardly extending supports mounted on theinner side of the terminal member, a cathode fixedly mounted on one ofthe supports, a first grid fixedly mounted on the other support andencircling the cathode, a relatively heavy partly conical supportingplate spaced outwardly from the terminal member, a second grid locatedbetween the cathode and first grid, means rigidly affixed to the plateand freely penetrating the terminal member and having the second gridfirmly mounted thereon, the unsupported ends of the cathode and bothgrids carrying apertured caps, and a nonconductive cylinder of heatexpandable ceramic material mounted in said caps and retaining thecathode and grids immovably in assembled spaced relation.

2. An electron tube comprisig a glass bulb, a relatively heavysubstantially frusto-conical end member sealed to one end of the bulb, atubular anode mounted at one end adjacent the seal between the endmember and bulb, an inverse relatively heavy frusto-conical terminalmember sealed to the opposite end of the bulb, a pair of rigidsubstantially frusto-conical inwardly extending supports mounted on theinner side of the terminal member, a cathode fixedly mounted on one ofthe supports, a first grid fixedly mounted on the other support andencircling the cathode, a relatively heavy artly conical supportingplate spaced outwardly from the terminal member, a second grid locatedbetween the cathode and first grid, means rigidly afiixed to the plateand freely penetrating the terminal member and having the second gridfirmly mounted thereon, the unsupported ends of the cathode and bothgrids carrying apertured caps, and a nonconductive cylinder of heatexpandable ceramic material mounted in said caps and retaining thecathode and grids immovably in assembled spaced relation, said cylinderbeing of a material having a coefficient of expansion greater than thatof the caps for expanding into tight engagement with said caps whenheated during operation of the tube.

3. An electron tube comprising a glass bulb, a relatively heavysubstantially frusto-conical end member sealed to one end of the bulb, atubular anode mounted at one end adjacent the seal between the endmember and bulb, an inverse relatively heavy frusto-conical terminalmember sealed to the opposite end of the bulb, a pair of rigidsubstantially frusto-conical inwardly extending supports mounted on theinner side of the terminal member, a cathode fixedly mounted on one ofthe supports, a first grid fixedly mounted on the other support andencircling the cathode, a relatively heavy partly conical supportingplate spaced outwardly from the terminal member, a second grid locatedbetween the cathode and first grid, and support means for the secondgrid rigidly afiixed at one end to the plate and freely penetrating theterminal member and having the second grid firmly mounted on theopposite end thereof, the supporting plate and terminal member havingconcentric apertures therein, and a nonconductive block of heatexpandable ceramic material mounted in said apertures for retaining theplate and terminal member in assembled spaced relation.

4. An electron tube comprising a glass bulb, a relatively heavysubstantially frusto-conical end member sealed to one end of the bulb, atubular anode mounted at one end adjacent the seal between the endmember and bulb, an inverse relatively heavy frusto-conical terminalmember sealed to the opposite end of the bulb, a pair of rigidsubstantially frusto-conical inwardly extending supports mounted on theinner side of the terminal member, a cathode fixedly mounted on one ofthe supports, a first grid fixedly mounted on the other support andencircling the cathode, a relatively heavy partly conical supportingplate spaced outwardly from the terminal member, a second grid locatedbetween the cathode and first grid, and support means for the secondg-rid rigidly afiixed at one end to the plate and freely penetrating theterminal member and having the second grid firmly mounted on theopposite end thereof, the supporting plate and terminal member havingconcentric apertures therein, and a nonconductive block of heatexpandable ceramic material mounted in said apertures for retaining theplate and terminal member in assembled spaced relation, saidnonconductive block having a coefficient of expansion greater than thatof the supporting plate and terminal for expanding into tight engagementtherewith when heated during operation of the tube.

5. An electron tube comprising a glass bulb having an anode at one endand an apertured cathode terminal at the other end, a hollow cylindricalcathode mounted at one end on said terminal, a nonconductive block ofheat expandable ceramic material having a coefficient of expansiongreater than that of the terminal mounted in the aperture in theterminal, and a heater within the cathode having one end attached to theunsupported end of the cathode and supported at its other end by meanscarried firmly by and penetrating the nonconductive block.

6. An electron tube comprising a glass bulb having an anode in one endand a cathode in the other end, a terminal plate for the cathode sealedto the cathode end of the bulb and having an annular portion which isprovided with an inwardly inclined inner surface of restricted length inan axial direction between the cathode and the seal to the bulb, a gridencircling the cathode, a substantially frusto-conical member having thegrid mounted on its smaller end, the larger end of the member having itsinner surface interfitting with said inclined inner surface of theplate, means for fixedly retaining the member on the plate, said gridbeing comprised of a plurality of longitudinally extending andrelatively thin elements spaced at a predetermined distance from andparallel to the cathode, and at least one spiral winding connecting saidelements and fixedly attached to each thereof to suppress resonantfrequencies in the elements.

References Cited by the Examiner UNITED STATES PATENTS 2,513,277 7/1950Best 313-258 X 2,901,657 8/1959 Stuart 3l3257 3,028,516 4/1962 Foote etal 313-250 X 3,041,495 6/1962 Knight et al. 313265 X 3,132,274 5/1964Kendall 313250 X 3,172,001 3/1965 Gaylord 313-250 X JOHN W. HUCKERT,Primary Examiner.

A. I JAMES, Assistant Examiner.

1. AN ELECTRON TUBE COMPRISING A GLASS BULB, A RELATIVELY HEAVY SUBSTANTIALLY FRUSTO-CONICAL END MEMBER SEALED TO ONE END OF THE BULB, A TUBULAR ANODE MOUNTED AT ONE END ADJACENT THE SEAL BETWEEN THE END MEMBER AND BULB, AN INVERSE RELATIVELY HEAVY RUSTO-CONICAL TERMINAL MEMBER SEALED TO THE OPPOSITE END OF THE BULB, A PAIR OF RIGID SUBSTANTIALLY FRUSTO-CONICAL INWARDLY EXTENDING SUPPORTS MOUNTED ON THE INNER SIDE OF THE TERMINAL MEMBER, A CATHODE FIXEDLY MOUNTED ON ONE OF THE SUPPORTS, A FIRST GRID FIXEDLY MOUNTED ON THE OTHER SUPPORT AND ENCIRCLING THE CATHODE, A RELATIVELY HEAVY PARTLY CONICAL SUPPORTING PLATE SPACED OUTWARDLY FROM THE TERMINAL MEMBER, A SECOND GRID LOCATED BETWEEN THE CATHODE AND FIRST GRID, MEANS RIGIDLY AFFIXED TO THE PLATE AND FREELY PENETRATING THE TERMINAL MEMBER AND HAVING THE SECOND GRID FIRMLY MOUNTED THEREON, THE UNSUPPORTED ENDS OF THE CATHODE AND BOTH GRIDS CARRYING APERTURED CAPS, AND A NONCONDUCTIVE CYLINDER OF HEAT EXPANDABLE CERAMIC MATERIAL MOUNTED IN SAID CAPS AND RETAINING THE CATHODE AND GRIDS IMMOVABLY IN ASSEMBLED SPACED RELATION. 